Add IDs to all headings on a page in WordPress

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<?php
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add_filter('the_content', 'add_id_attribute_to_headings');
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function add_id_attribute_to_headings($content): string {
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  return preg_replace_callback('#<(h[1-6])(.*?)>(.*?)</(h[1-6])>#', 'add_id_attribute_to_heading_callback', $content);
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}
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function add_id_attribute_to_heading_callback($match): string {
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  [$full, $el_start, $attributes, $content, $el_end] = $match;
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  if (str_contains($full, ' id="')) {
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    return $full;
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  }
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  $id = sanitize_title_with_dashes($content);
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  return '<{$el_start} id="{$id}" {$attributes}>{$content}</{$el_end}>';
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}